T-cell polyfunctionality reconstitution after modified anti-thymocyte globulin plus post-transplant cyclophosphamide in allogeneic hematopoietic stem cell transplantation

Objective Anti-thymocyte globulin combined with post-transplant cyclophosphamide (ATG/PTCy) is increasingly used for graft-versus-host disease (GvHD) prophylaxis; however, functional immune reconstitution after this regimen remains insufficiently characterized. Conventional immune monitoring based on absolute cell counts may not adequately reflect immune competence. Methods We retrospectively analyzed 76 patients who received ATG/PTCy (ATG, 2.5 mg/kg/day on days −2 and −1; cyclophosphamide, 50 mg/kg on day +3) following allogeneic peripheral blood stem cell transplantation. Peripheral blood mononuclear cells collected on days +30, +60, +90, +180, and +360 were stimulated with Staphylococcal enterotoxin B (SEB), and T-cell functionality was assessed using COMPASS-derived functionality scores (FS) and polyfunctionality scores (PFS). Associations between immune reconstitution and acute GvHD (aGvHD), chronic GvHD (cGvHD), viral reactivation, and bloodstream infection were assessed. Results Within 180 days after transplantation, 34.2% of patients developed aGvHD, including 25.0% with Grade II–IV aGvHD, and 61.8% experienced cytomegalovirus (CMV) reactivation. Peak CMV DNA loads >500 IU/mL were associated with higher incidence of aGvHD, Epstein–Barr virus (EBV) DNA detection, multiple viral infections, and bacteremia. Within 90 days, patients with Grade II–IV aGvHD showed lower CD4+ and CD8+ FS and PFS than those without Grade II–IV aGvHD. Higher CMV DNA levels were associated with impaired T-cell function at days +90 and +180. At day +60, a trend toward an interaction between aGvHD and CMV reactivation were observed for CD8+ T-cell function. At day +180, higher CD8+ T-cell counts and functional activity were associated with increased odds of cGvHD, whereas higher CD4+ T-cell and B-cell levels were associated with lower odds. By day +360, higher B-cell proportions remained inversely associated with cGvHD, whereas CD4+ T-cell levels showed no significant association. Conclusions Functional immune monitoring may complement immune cell enumeration and contribute to individualized post-transplant risk assessment in patients receiving ATG/PTCy-based allo-HSCT.